1. Field of the Invention
The present invention relates to an ignition device for a high speed burner of the cold nozzle type.
It relates more particularly, but not exclusively to a burner of this kind including:
a conventional type injector formed by the combination of an injection nozzle for a pressurized fuel gas, for example propane, a mixer duct into which said nozzle feeds and orifices opening to the free air, through which the air is sucked into the duct by venturi effect, is mixed with the fuel gas and is accelerated in the duct so as to form a high speed flow of a gaseous mixture;
an equation chamber, into which the injector opens, this adaptation chamber possibly having a bell mouth shape ending in an orifice having an outwardly curved grid;
an ignition chamber in which combustion of the gaseous mixture is initiated, which leaves at high speed through the perforations of the grid, this ignition chamber being formed by a tubular element extending the adaptation chamber; and
deflection means equipping the external opening of the ignition chamber and oriented so as to converge towards each other from opposite zones of said opening.
2. Description of the Prior Art
In this type of burner the beginning of the flame inside the ignition chamber is generated by the gaseous mixture jets produced by the central perforations of the grid which undergo an expansion phenomenon and slow down. Inside the ignition chamber, the nascent flame of a substantially parabolic shape occupies only a fraction of this chamber. It leaves the burner at high speed while passing between the deflectors to be then propagated in the free air while generating, beyond its leading front, a flow of hot air propagating axially with respect to the burner.
The effect of the cold nozzle is then due to the interaction of the lateral parts of the grid, of the walls of the ignition chamber and, to a lesser extent, of the deflectors.
In fact, the lateral parts of the grid form with said walls wedge shape spaces which constitute dead spaces in which the flame cannot propagate. These dead spaces are traversed by the gaseous mixture jets coming from the perforations of the lateral parts of the grid which then run into each other and flow as a gas flow over the walls of the ignition chamber over the deflectors. This gas flow, not ignited, then provides heat insulation and continuous cooling of the walls which cannot therefore overheat. This phenomenon further extends to the deflectors which are then not licked by the flame and which are then not subject to any overheating.
For igniting the flame, an ignition plug has also been proposed mounted in a tubular housing opening into the ignition chamber through an orifice provided at a position on the wall of said chamber situated in line with the lateral zone of the grid.
However, in use it has proved that this solution has serious drawbacks. In fact, the tubular housing for the gas flow emitted by the perforations of the grid. Thus, a permanent self sustained combustion of the gas flow may be formed at this level of the cavity, causing overheating of the wall of the ignition chamber, which is contrary to the desired aim.